Yes, all thoughts about data-unavailability and unavailable blocks concern the Plasma chain only. As you correctly said, Eve and the Plasma operator may collude. But they can only affect the visibility and content of the Plasma chain.
An eclipse attack on Alice is also a possible scenario (not limited to Plasma, it could affect main-net transactions and state channels), but the cost of doing so is probably a manyfold of the value locked in the Plasma chain. Hence I have not considered such attacks here.
The Plasma Leap write-up has some ideas how to deal with state under subjective data-availability assumptions.